1. Field of the Invention
The present application relates to the field of radar systems for motor vehicles.
2. Description of the Related Art
Vehicle safety systems can generally be categorized as either crash protection systems or accident avoidance systems. Crash protection safety systems can minimize the effects of an accident, but an effective accident avoidance system can allow a driver to avoid an accident altogether. This is the basic philosophy that makes automotive radar so attractive as a potential accident avoidance system. Radar systems are particularly suited to backup warning systems that warn the driver that the vehicle is about to back into an object such as a child or another vehicle. Radar systems are also particularly suited to side-object warning systems (also known as blind-spot warning systems) that warn the driver not to change lanes because another vehicle is in the region known as the driver""s xe2x80x9cblind-spotxe2x80x9d or side-object region. The left side-object region is typically slightly behind and to the left of the driver""s vehicle. The right side-object region is typically slightly behind and to the right of the driver""s vehicle. Many lane-change collisions occur because a driver of a first vehicle desiring to change lanes does not see a second vehicle in an adjacent lane, especially when the front bumper of the second vehicle is beside the rear portion of the first vehicle.
Yet, in spite of the obvious desirability, and decades of research, automotive warning radars have not been widely used. To date, automotive radar warning systems have been either too primitive to provide useful information to the driver, or too expensive. Many vehicle radar warning systems in the prior art merely detect the presence of a target, any target, without providing the driver with any information as to the nature or location of the target. One target characteristic of great importance is the distance from the radar to the target (the downrange distance). Many of the simple, inexpensive, radars proposed for automotive use provided no downrange, information. Those radars that do provide downrange information typically do not provide accurate downrange information for multiple targets because the radars cannot discriminate between multiple targets. Radars that do attempt to discriminate between multiple targets are generally too costly for most drivers to afford.
The simplest automotive radar systems use a Continuous Wave (CW) radar in which a transmitter continuously transmits energy at a single frequency. The transmitted energy is reflected by a target object and received by the radar receiver. The received signal is Doppler shifted by movement of the target object relative to the radar. The CW receiver filters out any returns without a Doppler shift (i.e., targets which are not moving with respect to the radar), When the receiver detects the presence of a Doppler shifted signal, the receiver sends a signal to a warning device that warns the driver. Unfortunately, this type of radar provides no downrange information, and so the driver does not know how close the object is to the vehicle.
Another type of radar found in prior art radar warning systems is a two-frequency CW radar. The two-frequency CW radar transmits energy at a first frequency and a second frequency. The transmitted energy is reflected by a target object and received by a two-frequency CW receiver. The receiver measures the difference between the phase of the signal received at the first frequency and the phase of the signal received at the second frequency. The distance to the target object can be calculated from the measured phase difference. Unfortunately, the two-frequency CW radar performs poorly when there are multiple targets within the field of view of the radar. The simple two frequency system cannot discriminate between two targets at different ranges and thus, the range measurements obtained from a two frequency CW system in the presence of multiple targets is unreliable.
Frequency Modulated Continuous Wave (FMCW) radars have also been used in automotive applications, especially for forward looking systems such as automatic braking and automated cruise control. In an FMCW radar, the frequency of the transmitted signal is swept over time from a starting frequency to an ending frequency. The transmitted signal is reflected by a target and received by the FMCW receiver. The signal received by the receiver is delayed in time according to the travel time of an electromagnetic wave from the transmitter, to the target, and back to the receiver. Since the frequency of the transmitted signal is being varied over time, at any instant in time the frequency of the received signal will be slightly different than the frequency of the transmitted signal. In the absence of Doppler shifting, the distance to the target can be calculated by comparing the frequency of the received signal to the frequency of the transmitted signal. The presence of Doppler shifting will shift the frequency of the received signal and make the target appear to be closer or further away than it actually is.
UltraWideband (UWB) impulse radars have also been proposed for use in vehicle warning systems. However, UWB radars are undesirable because these radars transmit energy over very wide bandwidths and create electromagnetic interference which can interfere with other radio frequency systems such as broadcast radio, television, cellular phones, etc. UWB radars must operate at very low power in order to avoid violating rules promulgated by the Federal Communications Commission (FCC). In addition, UWB radars require antennas that can be used with the very broadband signals transmitted and received by the radar. These very broad band antennas can be difficult to design and build.
Additional problems arise when mounting backup warning radars to large trucks, delivery vans, construction vehicles, and semi-trailers, etc. (collectively xe2x80x9ctrucksxe2x80x9d). Existing backup warning systems and lane-change aids for trucks are expensive and difficult to retrofit into existing truck fleets. Installation of the radar units requires skilled personnel and several hours to install. Existing systems have sensors that must be carefully oriented in order to have the correct field of view. Moreover, signal wires must be run from the radar sensors on the back of the truck to the driver interface in the cab of the truck. For trailers and semi-trailers, these signal wires require the installation of a connector between the tractor and the trailer. This may be especially problematic when the owner of a large fleet of trucks desires to upgrade some or all of the fleet with backup warning radars.
The present invention solves these and other problems by providing a radar system that can track and discriminate multiple Doppler shifted targets while using a transmitted signal which can be adapted to fit within the radar bands allocated by the FCC. The radar can provide crossrange and downrange information on multiple targets and is not confused by the presence of Doppler shifting. The radar is simple to build, low in cost, and is well suited to vehicular applications. The radar system is particularly suited to backup warning systems and side-object warning systems in which the driver of a vehicle needs to be warned of an impending collision with an object which is out of the driver""s immediate field of view. The present radar minimizes many of the problems found in the prior art by transmitting a pulsed carrier frequency and using a receiver with programmable delays and programmable gain.
The receiver uses a range search algorithm to detect and sort targets at various ranges within the field of view of the radar. Each target range corresponds to a particular delay and gain setting. For each target range, the search algorithm sets the proper time delay and gain setting. Targets within the selected range are detected and catalogued. A display is used to warn the operator of the vehicle of the presence of targets at the various ranges. The warning may be visual and/or audible. Crossrange information is obtained by using multiple radar sensors. Each radar sensor detects targets in a different region around the vehicle. In some embodiments, these regions overlap such that a target may be detected by more than one radar sensor. In one embodiment, the radar is designed to ignore objects, which are stationary with respect to the radar (i.e., targets without Doppler shift). Stationary targets, such as reflections from other parts of the vehicle on which the radar is mounted, usually represent little risk of collision and thus are desirably ignored.
The present radar system may be used inside the passenger compartment of a vehicle to detect the presence, size, position, velocity, and/or acceleration of passengers or other objects within the vehicle. Such information can be used, for example, in an intelligent airbag deployment system. The radar may also be used inside the passenger compartment to as part of a throttle position sensing system, which detects the throttle position by detecting the location of a portion of the mechanical throttle linkage, such as, for example, the location of the xe2x80x9cgas pedal.xe2x80x9d In a similar fashion, the radar may also be used to detect the position of the brake pedal, seats, etc.
The radar may be used outside the passenger compartment to detect objects behind the vehicle, beside the vehicle, in front of the vehicle, etc. The radar may be used as part of an active suspension system. In one embodiment, the radar may be used to measure the height of the vehicle above the road surface. The radar may also be used to detect the position, velocity, and acceleration of portions of the vehicle suspension system. The radar may also be used to detect anomalies or changes in the road surface. Such anomalies include changes in surface texture, holes (e.g., xe2x80x9cpot-holesxe2x80x9d), etc. Information on road surface anomalies may be supplied to the driver, to an active suspension system, etc.
In one embodiment, several intelligent radar sensors are placed in and around the vehicle and each radar sensor is connected to a vehicle information bus. Each radar sensor measures targets within its field of view and broadcasts the radar target information to the vehicle information bus. Other vehicle systems, such as, for example, display units, suspension units, airbag units, etc. are also connected to the information bus. These other vehicle systems receive the radar target information and use the information to improve the operation, safety, and/or convenience of the vehicle.
The radar sensor may further compute a time to impact based on a downrange distance to a target and a relative velocity between the target and the radar sensor. The radar may provide a field of view that corresponds approximately to the side-object region can be used as both a collision avoidance system and a lane-change aid.
In yet another embodiment, the radar may include an audible warning device configured to project an audible warning signal which varies according to the downrange distance of the closest target, or the relative velocity between the radar and a target, or the time to impact between the radar and a target.
Yet another embodiment of the present invention is an intelligent display for providing information to a driver of a vehicle. The intelligent display includes a sensory display, such as an audible or visual display, and a control processor. The control processor is configured to receive sensor information from a vehicle information bus. The sensor information includes data measured by one or more sensors, such as radar sensors, connected to the information bus. The control processor prioritizes the sensor information and formats the sensory display based on the sensor information.
In yet another embodiment of the present invention, the radar sensor may be integrated into a standard taillight housing assembly for a truck or trailer. Integrating the radar into the taillight housing greatly simplifies the mounting and maintenance problems associated with adding a backup warning system to trucks. The radar sensors for a backup warning system, and/or radar sensors for a lane-change aid may be integrated into one or more of the taillights. In some embodiments, a backup warning radar sensor in the integrated radar-taillight assembly draws power from the power supplied to the reverse light. In another embodiment, the radar sensor in a lane-change aid draws power from the power supplied to a signal light.
In some embodiments, the radar sensor in the integrated radar-taillight assembly communicates with a central control unit by using current-carrier networking. In current carrier networking, the data is modulated onto an alternating current carrier, which is then coupled onto the standard 12 volt or 24 volt direct current (DC) wiring found in the truck. In this manner, the integrated radar-taillight assembly can easily be installed on a trailer or semi-trailer in only a few moments time, by a relatively unskilled worker. Moreover, since the current-carrier network uses the existing wiring, a communication link between the radar sensor and a central control unit is easily provided without extensive modifications or additional wiring in the truck or trailer. A control unit in the cab (or tractor) couples to the taillight wiring in order to communicate with the radar sensor in the remote radar-taillight assembly. The control unit can coordinate the operation of several radar-taillight assemblies and operate an audio-visual display for the driver.
The integrated radar-taillight assembly does not require special purpose mounting, but rather, can use the existing taillight mounting locations. The existing mounting locations are usually provided in relatively protected locations and are available on virtually all trucks. Moreover, the mounting locations are desirably wired for power to service the existing taillights. Hiding the radar sensor in the taillight assembly also helps to prevent theft and vandalism.
Tractors are often used with multiple trailers. Thus, in some embodiments, the driver interface in the cab provides different types of data depending upon the type of sensor installed in the trailer. For example, the maximum downrange distance or the boundaries of the range gates may desirably be different in a trailer that is typically backed up to a dock as compared to a trailer that typically is unloaded at a ramp.
The current-carrier network provides a single control unit interface to one or more radar sensors. Many types of sensors may transmit display commands to the driver interface. For example, a tractor may be connected to a trailer having only a backup warning system, a tractor having only a lane-change aid system, or a trailer having both. In each case, the central control unit and the user display in the cab will adapt to, and show data based on, the available sensors.
An optical sensor or a current sensor may be provided in the integrated radar-taillight assembly to warn the driver that one or more of the taillights have failed (e.g., burned out).
In yet another embodiment, the radar-taillight assembly uses an array of Light Emitting Diodes (LEDs) in lieu of the more traditional incandescent bulb for the taillights. The LEDs are more reliable, longer lived, provide lower operating temperature, and are more compact than incandescent lamps. An array of LEDs provides considerable fault tolerance, since the failure of a few LEDs in an array will not seriously affect the amount of light produced by the array.
In one embodiment, manufacturability and stability of the radar system are improved by replacing analog processing with digital processing The amount of digital data is reduced by controlling the number of analog-to-digital conversions. Digital samples are produced during desired time periods corresponding to desired target ranges, and digital samples are not produced during other periods corresponding to other target ranges.
In one embodiment, the digital samples are produced in by using fast analog sampling followed by lowpass filtering and slow digital sampling. In another embodiment, the digital samples are produced by fast digital sampling and a digital detector in a Digital Signal Processor (DSP). The DSP processes the digital samples (corresponding to a desired target range) in response to a trigger pulse from a time delay. This reduces the amount of data that the DSP will have to process, thereby reducing the complexity and cost of the radar system. In yet another embodiment, an analog-to-digital converter produces digital samples from an intermediate frequency signal in response to a programmable time delay. The programmable time delay selects samples corresponding to a desired target range (e.g., a desired downrange). Yet another aspect of the invention is a lane-change aid system that detect objects (targets) in a driver""s blindspot to help the driver make lane-change maneuvers safer for all and less stressful for the driver. One or more lane-change radars detect targets in side-object regions of the vehicle. The radar sensor allows the lane-change system to distinguish between objects that are relatively close and objects that are relatively far away.
To further reduce false alarms, one embodiment of the lane change aid system uses the speed of the vehicle to determine a maximum target distance for audible alarms. For a given vehicle speed, if a target is detected outside the maximum distance for that given speed, then no audible alarm is issued. Conversely, if a target is detected inside the maximum distance for a given speed, then an audible alarm is issued. In one embodiment, an alarm is issued when an object is detected on the left side of the vehicle and the left turn signal is activated. Similarly, an alarm is issued when an object is detected on the right side of the vehicle and the right turn signal is activated